1. Technical Field
The present invention relates to an electrochromic panel (EC panel) in which it is possible to alternate between a colored state and a colorless state when the panel is installed onto a rear-view mirror of a vehicle and a DC voltage polarity is applied in an inverted fashion. More specifically, the present invention pertains to a drive unit that provides a fail-safe function as well as an easy one-touch operation for alternating between the colored and colorless states.
2. Description of Prior Art
For example, when a passenger vehicle or a truck is driven at night, there are several cases in which the light beams from the head lamps of following vehicles reflect against the rear-view mirrors (both internal and external) and enter the driver's field of view, causing the driver to experience temporary blindness. Therefore, in order to solve such a problem EC panels (electrochromic panels) have been conventionally installed onto the glass substrates used for rear-view mirrors, and by applying a DC voltage to the EC panels, it has become possible to reduce the reflectivity and prevent this temporary blindness from occurring.
FIG. 3 shows one of conventional circuits that has been used as a drive circuit for EC panels, and by applying a switchable DC voltage polarity outputted from a DC power source 12 to the input terminal of an EC panel 11 as shown in FIG. 3, it is possible to obtain a blindness prevention state (hereinafter referred to as the colored state) by reducing the reflectivity of the rear-view mirror, as well as return the rear-view mirror from this colored state to its original state of reflectivity (hereinafter referred to as the colorless state).
In other words, through the operation of a two-way switch 13 (13-1 and 13-2) as shown in FIG. 3, connections are made between contacts 13-1c and 13-1a, as well as between contacts 13-2c and 13-2a, such that voltage is applied in a forward direction to the input terminal of the EC panel 11, making it possible for the EC panel 11 to be in the colored state whereby the reflectivity is reduced. Conversely, by operating the switch 13 in a reverse fashion such that connections are made between contacts 13-1c and 13-1b, as well as between contacts 13-2c and 13-2b, the voltage is applied in a reverse direction to the input terminal of the EC panel 11, causing it to return to its colorless state. Accordingly, through the operation of this switch 13, the driver can change the reflectivity of a rear-view mirror and thus prevent temporary blindness from occurring as a result of light beams from the head lamps of following vehicles being reflected against the rear-view mirror during night driving.
However, since the use of the aforementioned EC panel drive circuit makes it necessary for the driver to press and hold the two-way switch 13 for a set period of time in order to change the EC panel 11 to and from the colored and colorless states, this operation may be burdensome for the driver. That is to say, the disadvantage here is that once the voltage is applied to the EC panel 11, it does not immediately change it to either the colored or colorless state, but rather, it gradually changes to or from either state through the application of voltage in a forward or reverse direction for a set period of time, thus making it necessary for the driver to press and hold the two-way switch 13.
Furthermore, since a two-way switch 13 is used in the case of the EC panel drive circuit shown in FIG. 3 in order to switch the EC panel 11 back and forth between the colored and colorless states, it is impossible for a fail-safe function to actuate in cases where errors occur during the operation of the switch.
A detailed explanation of this is given below. Given the colored state of the EC panel 11, in which case the reflectivity of the rear-view mirror is reduced, operating the switch 13 so that connections are made between contacts 13-1c and 13-1b as well as between contacts 13-2c and 13-2b will cause the EC panel 11 to return to its colorless state. When a problem occurs in this case, namely, a drop in the level of voltage from the DC power source 12, it becomes impossible for the EC panel 11 to return to the colorless state from the colored state.
Thus, in comparing the safety between the colored state and the colorless state of the EC panel 11, it is apparent that the colorless state is the safer of the two. Therefore, when considering a fail-safe function in the case where a failure has occurred, the colorless state of the EC panel 11 is preferable. However, as noted above, in conventional cases of drive units used for the EC panel 11 in which a drop has occurred in the level of the voltage supplied from the DC power source 12, there occurs a problem that the EC panel 11 has become frozen in the colored state, and a fail-safe function which would allow the EC panel to return to its original state has not been realized.
In addition, a characteristic of the EC panel 11 is a change in the level of color in response to the amount of DC voltage applied. However, in the case of the EC panel drive unit shown in FIG. 3, the value of the voltage level applied to the EC panel 11 is fixed, and as a result, the level of color is always fixed. Accordingly, the disadvantage here is not only that the driver is unable to set the reflectivity of the rear-view mirror to a desired level, but also that it is impossible to change the reflectivity in response to the brightness of the surroundings.
As described above, in conventional drive units for EC panels, it is necessary to press and hold a two-way switch 13 in order to change the EC panel 11 to the colored state as well as to the colorless state, and this is a disadvantage from the standpoint of operation.
Furthermore, since no fail-safe function, such as the ability for the EC panel 11 to return to the colorless state in the case where there is a drop in the level of voltage from the DC power source 12 when the EC panel 11 is in the colored state, is available, the loss in the level of safety is a disadvantage. Also, since the value of the voltage applied to the EC panel 11 is fixed, the problem of the reflectivity of the rear-view mirror not being able to be set to a desired level has occurred.
This invention is designed to solve these conventional problems, and its objective is to obtain the ability to switch an EC panel back and forth between a colored state and a colorless state using a one-touch operation. Furthermore, the present invention makes it possible to achieve a fail-safe function and provide an EC panel drive unit for rear-view mirrors in which the reflectivity can be changed.